The mechanical load-bearing capacity of foams is comparatively low, particularly in relation to tensile forces. If foam mouldings are to be connected to other components so as to be capable of bearing tensile loads it is therefore conventional in the state of the art either to undertake adhesion-bonding over a large area or to make use of anchoring elements in order to guarantee distribution of the forces over a wide area and to avoid point-focal loads that would result in fissure of the foam.
Particularly in vehicle construction, cushioning elements frequently consist of a central foam moulding, the surface of which is provided with a cover, usually a fabric or leather. In order to permit fastening of the cover at individual points or along a seam with the foam core there are integrally moulded within the foam one or more wires, to which the cover is connected by means of fastening elements, for example by filaments or hooks. By virtue of a taught connection, indentations are formed in the region of the junction points on the surface of the cushion which improve the fixation of the cover and contribute to the optical and functional design of the surface. With a suitable shape of the foaming tool it is possible to ensure that the points of attachment to the wire are freely accessible through recesses in the moulding, so that establishment of the connection is alleviated. By way of foams, use is made predominantly of polyurethanes which are produced by polyaddition of polyhydric alcohols with polyisocyanates. In this connection a reaction of the isocyanate with the hydroxyl group characterising the alcohol takes place. This state of the art can be inferred from U.S. Pat. No. 3,649,974, the disclosure of which is hereby incorporated by reference.
The wires that are customary for anchoring adhere to the foam comparatively poorly--ie, the connection is effected almost exclusively by means of the form closure brought about by the integral moulding within the foam. With a view to achieving an adequate load-bearing capacity a sufficient cross-section of the wire is therefore required which, however, results in an increased weight which is disadvantageous for reasons of energy economy, particularly in vehicle construction. Moreover it is necessary to keep wires of various lengths in stock for different applications, considerably increasing the effort expended on storage. Finally, after they have been used, foam parts are frequently recycled by being shredded into flakes or by chemical dissolution. Both processes are impaired or hindered by metallic anchoring elements, so the wires have to be removed beforehand in elaborate manner.